1. Field of the Invention
The present invention relates to amyloid precursor-like proteins (APLPs) including APLP1 and APLP2; products and processes involved in the cloning, preparation, and expression of genes for APLPs; antibodies with specificity to these proteins and to diagnostic and therapeutic uses thereof.
2. Brief Description of the Background Art
Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the presence of neurofibrillary tangles, and amyloid in the form of senile plaques and blood vessel deposits in the brain. The main component of amyloid is A.beta., a 39-43 amino acid peptide derived from a larger amyloid precursor protein (APP) encoded by a gene on chromosome 21 (Glenner and Wong, Biochem. Biophys. Res. Commun. 120:885-890 (1984); Goldgaber et al., Science 235:877-880 (1987); Kang et al., Nature 325:733-736 (1987); Robakis et al., Proc. Natl. Acad. Sci. USA 84:4190-4194 (1987); Tanzi et al., Science 235:880-884 (1987)). A proportion of AD is inherited (reviewed in St. George-Hyslop et al., Neurobiol. Aging 10:417-425 (1989)) and the familial form (FAD) has been clearly shown to be a genetically heterogeneous disorder (Schellenberg et al., Science 241:1507-1510(1988); St. George-Hyslop et al., Nature 347:194-197 (1990)). An early-onset (&lt;65 years of age) FAD locus was mapped to chromosome 21 (St. George-Hyslop et al., Science 235:885-889 (1987)), and a small percentage (less than 3%) of FAD is linked to point mutations within the APP gene (Goate et al., Nature 349:704-706 (1991); Murrell et al., Science 254:97-99 (1991); Chartier-Harlin et al., Nature 353:884-846 (1992); Tanzi and Hyman, Ann. N. Y. Acad. Sci 640:149-154 (1992); Mullan et al., Nature Genetics 2:340-342 (1992)). More recently, studies revealed the presence of a major early-onset FAD locus on chromosome 14 (Mullan et al., Nature Genetics 2:340-342 (1992); Schellenberg et al., Science 258:668-673 (1992); St. George-Hyslop et al., Nature Genetics: in press (1992); Broeckhoven et al., Nature Genetics 2:335-339 (1992)). Some early-onset FAD pedigrees do not demonstrate linkage to either the APP gene or chromosome 14 (Schellenberg et al., Science 241:1507-1510(1988); St. George-Hyslop et al., Nature 347:194-197 (1990); Schellenberg et al., Science 258:668-673 (1992); Tanzi, R. E., Am. J. Human Genet. 51:273-282 (1992)).
A subset of, but not all late-onset (&gt;65 years of age) FAD pedigrees appear to be linked to a locus on chromosome 19 (Pericak-Vance et al.,Am. J. Hum. Genet. 48, 1034-1050(1991)). Therefore, in addition to genes on chromosomes 14, 19 and 21 there would appear to be at least two additional FAD loci that remain unmapped. Candidate genes for other FAD loci include potential APP gene homologues which might either serve as alternative substrates for amyloid formation, or interfere with normal processing of APP.
APP resembles an integral membrane protein with a small cytoplasmic C-terminal domain and a larger, extracellular N-terminal domain (Kang et al., Nature 325:733-736 (1987)). The APP gene produces at least six transcripts (Ponte et al., Nature 331:525-527 (1988); Tanzi et al., Nature 331:528-530 (1988); Kitaguchi et al., Nature 331:530-532; De Sauvage et al., Science 245:651-655 (1989); Jacobsen et al., Neurobiol. Aging 12:575-583 (1991); Konig et al., J. Biol. chem. 267:19804-19809 (1992)), five of which include an alternatively spliced exon encoding a Kunitz type protease inhibitor domain. APP appears to be processed through at least two pathways. A secretory pathway results in the cleavage of APP at a site near the membrane of extracellular-junction, within the .beta.A4 domain (Esch et al., Science 248:1122-1124 (1990); Sisodia et al., Science 248:492-495 (1990)), and precludes the formation of A.beta.. Alternatively, processing in the endosomal-lysosomal pathway leads to the production of carboxy terminal derivatives that contain the A.beta. peptide (Estus et al., Science 255:726-728 (1991); Golde et al., Science 255:728-730(1991); Haass et al., Science 357:500-503 (1992)). More recently, it has been demonstrated that A.beta. is generated in a soluble form by cultured cells (Haass et al., Nature 359:322-325 (1992); Sebubert et al., Nature 359:325-327 (1992); Shoji et al., Science 258:126-129 (1992)), although the exact pathway leading to the generation of soluble A.beta. is unknown. Presumably, a precise balance among these pathways must be maintained in order to avoid the overproduction of amyloidogenic fragments.
It has previously been hypothesized that proteins resembling APP in amino acid sequence and overall structure may interact with, and effectively compete for factors playing a role in the maturation and/or metabolism of APP (Wasco et al., Genomics: in press (1992); Wasco et al., Proc. Natl. Acad. Sci. USA 89:10758-10762 (1992)). Recent evidence indicates that APP is a member of a family of proteins with specific domains that have been remarkably well conserved.
cDNA clones predict that APP is a transmembrane protein with a small intracellular C-terminal domain and a larger, extracellular N-terminal domain (Goldgaber et al., Science 235:877-880(1987); Kang et al., Nature 325:733-736 (1987); Robakis et al., Proc. Natl. Acad. Sci. USA 84:4190-4194 (1987); and Tanzi et al., Science 235:880-884 (1987)). There are at least four forms of APP that result in proteins of 563, 695, 751 and 770 amino acids (De Sauvage et al., Science 245:651-653 (1989); Kitaguchi et al., Nature 331:530-532 (1988); Ponte et al., Nature 331:525-527 (1988); and Tanzi et al., Nature 331:528-530(1988)). At least three of these are the result of alternative splicing (Kitaguchi et al., Nature 331:530-532 (1988); Ponte et al., Nature 331:525-527 (1988); and Tanzi et al., Nature 331:528-530(1988)). The two larger forms of APP contain a 56 amino acid insert that has homology to the KuNa family of protease inhibitors (Kitaguchi et al., Nature 331:530-532 (1988); Ponte et al., Nature 331:525-527 (1988); and Tanzi et al., Nature 331:528-530(1988)).
One of the secreted forms of APP that contains a protease inhibitor domain has been found to be identical to protease nexin-II (Oltersdorf et al, J. Biol. Chem. 265:4492-4497 (1990); and Saitoh et al., Cell 58:615-622 (1989)).
The .beta.A4 domain spans the predicted membrane-extracellular junction of APP. How this peptide is liberated from the precursor protein in Alzheimer's disease remains unclear. Results from a number of laboratories suggest that normally the precursor protein is secreted via cleavage at sites that are at or near the membrane-extracellular junction, apparently within the .beta.A4-domain (Esch et al., Science 248:1122-1124 (1990); Selkoe et al., Proc. Natl. Acad. Sci. USA 85:7341-7345 (1988); Weidman et al., Cell 57:115-126 (1989); and Sisoda et al., Science 248:492-495 (1990)). If these findings are correct, normal processing of the secreted form of APP would preclude the formation of .beta.A4, and therefore, of amyloid itself. Such a model implies that .beta.A4 contained within the plaques and cerebrovascular deposits is the result of an abnormal processing event.